This invention relates generally to acousto-optic beam deflectors, and particularly to methods of fabricating acousto-optic beam deflectors of the type employing a stepped-array of transducers.
In the article entitled "Interaction Between Light and Sound," By Robert Adler, which appeared in the May 1967 issue of IEEE SPECTRUM, an acousto-optic beam deflector was proposed utilizing the Bragg reflection phenomenon. According to this principle a spatially-coherent, substantially monochromic light beam incident upon sound waves at a particular angle, which depends upon the wavelength of the light and sound, is defracted by the sound wave at this same angle. In other words, when light and sound interact at the Bragg angle the traveling sound waves act as if they were moving mirrors. Thus by altering the direction of sound wave propagation, a beam of coherent light incident upon the traveling sound waves may itself be deflected.
In order to maintain the proper Bragg angle relationship it is necessary to accompany changes in direction of sound propagation with changes in sound frequencies. A device which accomplishes this with both a sizable interaction area and frequency bandwidth is that known as an echelon or steppedarray acousto-optic beam deflector. This type beam deflector, as exemplified by that disclosed in U.S. Pat. No. 3,493,759, has heretofore comprised a series of individual transducers mounted upon a series of steps formed in a glass element affixed to an end of a light-sound interaction cell with each step offset from the next adjacent step by distance equal to half the wavelength of the sound employed at center frequency.
This type of beam steering device has the attribute of providing an acousto-optic interaction length which can be increased without sacrifice in bandwidth. Therefore, less power may be required in its operation for a given efficiency. Increase in interaction length also increases the cross-section of the acoustic beam which further reduces power density. Once fabricated, stepped-array acousto-optic beam deflectors have performed quite satisfactorily. Fabrication has been a limiting factor however due to the extremely small dimensions of the steps. Thus, the bonding, grinding, polishing and electroding required has made their formation quite tedious and costly.
Accordingly, it is a general object of the present invention to provide an improved method of fabricating a stepped-array acousto-optic beam deflector.
More specifically, it is an object of the invention to provide a method of fabricating a stepped-array acousto-optic beam deflector which does not mandate the formation of steps in situ upon a unitary element.
Another object of the invention is to provide a method of fabricating a stepped-array acousto-optic beam deflector with improved facility, accuracy and cost efficiency.